It is well-known in the building trades to install on a roof a drainage device that communicates with a drainpipe or leader below the surface of the roof, for removing rainwater and the like. Such a device must provide a watertight connection with the leader and with the surface of the roof, so that water is prevented from leaking below the roof and causing damage.
A typical type of roof drain has a dome type strainer with vertical drainage slots on all sides. The diameter of the strainer is greater than that of the vertical leader with which it is used. A horizontal ting portion that is flat on its bottom surface is integral with the base of the strainer. The ring portion extends inwardly of the domed portion of the strainer to define a drainage outlet that is slightly smaller in diameter than the leader. The ring portion also extends outwardly of the domed portion defining a flange.
In use, the ring portion of the strainer is mounted to a separate clamping ring that encircles the leader below the surface of the roof. The clamping ring has top and bottom flat horizontal ring portions that are similar in size to the strainer ting portion. Typically, the strainer has several lugs that protrude as extensions of the flange at its base. The clamping ting used with it has the same size or slightly larger openings in its top ting portion. The strainer is lowered onto the clamping ring such that the lugs pass through the openings in the top ring portion. The strainer is then turned so that the lugs are between the top and bottom ting portions. Thus, it cannot be directly lifted out of engagement with the leader. Bolts are used to secure the strainer ring portion to the top and bottom ting portions of the clamping ring, each bolt passing through all three ring portions. Such mounting must be watertight.
Separate mounting of the clamping ring and the strainer of this type of device requires skill. It is typically performed by a plumber, rather than by a roofer or by some unskilled individual.